A well-known image-forming apparatus includes a casing whose upper portion is formed with an opening, a top cover configured to open and close the opening and an LED head supported by the top cover and having an exposing surface facing downward. When the top cover is closed to mount a process cartridge including a photosensitive drum in the casing, the exposing surface of the LED head opposes the photosensitive drum to expose the photosensitive drum. Further, the LED head is retracted from the process cartridge when the top cover is opened, thereby enabling the process cartridge to be replaced easily.